Corruption in politics was described to me once as the grease that keeps the cogs of government turning. The importance difference is what type of grease is used. A government with low corruption uses a small amount of very clean grease, just enough, and only in the right places, to make the sticky gears turn. A government with high corruption will just drench every gear with very dirty crude oil, and if the gears seizes up they won't even notice.

In an ideal world the machine of government wouldn't need any corrupt grease or oil to keep turning but no one truely lives in that world, yet.